IO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL.98 



STORAGE OF SOLAR HEAT OR POWER 



I will now consider briefly some suggestions relating to the storage 

 of heat or of power from the sun. As everyone knows, heat is prone 

 to dissipate itself. There are no insulators against heat conduction 

 comparable in efficiency to those which prevent the flow of electricity. 

 My friend Dr. Cottrell, however, proposed to me a scheme which may 

 be worth a trial. He suggests a silo-shaped, cement-lined pit in the 

 ground, filled nearly to the top with dry coarse sand, and roofed over. 

 Above the sand lies a layer of perhaps 10 feet of glass wool, such as 

 is used for roof insulation. A pipe leading from the solar heater to 

 the center of the upper surface of the sand has an appropriate net- 

 work of branch pipes covering the surface. A similar network at the 

 bottom of the pile leads to an outlet pipe, and thence back to the 

 heater. An automatic pump which runs only while the focus tube is hot, 

 draws hot air through the solar heater into the top of the sand. Owing 

 to the notoriously bad conductivity of dry sand, and the high degree 

 of protection from upward convection and conduction offered by the 

 thick layer of glass wool, the sand pile receives the heat, and keeps 

 it in a horizontal layer. The heated layer gradually works down, till, 

 if the storage operation is very long-continued, the whole sand pile 

 becomes of nearly as high temperature as the air in the focus tube 

 itself. With a sand silo of sufficient capacity, Dr. Cottrell thinks the 

 efficiency would be so high that when the heat was drawn away, 

 perhaps months later, by reversing the circulation of air, the air 

 would come away from the top of the sand very nearly as hot as it 

 formerly entered. No one has tried this interesting scheme, but it 

 would be desirable to do so. Should it succeed, it might show the 

 way to use the heat of summer to warm one's house in winter. 



Electric storage batteries are so well known that it is unnecessary 

 to point out that solar power may be conserved thereby for night use. 

 It is the cost which shades this proposal. 



Chemical storage might be clone by electrolyzing water, and saving 

 the hydrogen to be burned in air with boilers to generate steam. This 

 involves the problem of successful use of hydrogen as a steaming fuel. 



Mechanical storage could be accomplished by pumping water to a 

 high level reservoir, to be used in a hydroelectric plant later. This 

 also looks costly, and difficult except in hilly country. 



Possibly best of all would be a heat storage within a pressure tank 

 filled with water, and surrounded by a thick envelope of glass wool. 

 The water, heated far above the boiling point, would supply steam 

 for hours of cloudiness or nigrit. 



